The integration of viral DNA into the host cells' DNA is a required step in the retroviral infection process. The aim of this proposal is to elucidate the oligomeric structure of the viral integrase protein (IN), which is responsible for this activity. The IN protein has been shown to be necessary and sufficient for the integration of DNA with LTR (long terminal repeat) ends into a target DNA, in vitro. The nature and composition of native IN complexes will be elucidated using a variety of techniques including gel filtration, chemical cross-linking, native gel electrophoresis, CD spectra and immunoprecipitation. Individual amino acid sequences that are required for multimerization will be determined, and confirmed by site-directed mutagenesis. Functional assays will also be used to examine the effects of these mutations on IN activity. The retroviral integrase has no cellular counterpart, and therefore represents a suitable target for intervention in the infection process. These studies will further our understanding of how protein structure is related to the mechanism of retroviral integration, and will aid the design of strategies to control retroviral replication.